Removal of alkali metal impurities from liquid diene polymers



United States Patent REMOVAL OF ALKALI METAL IlVIPURITlES FROM LIQUIDDIENE POLYMERS Paul F.'Wamer, Phillips, Tex., assignor to PhillipsPetroleum Company, a corporation of Delaware No Drawing. Filed 0a. 30,1958, Ser. No. 770,600

6Claims. or. 260-290) This invention relates .to the removal of alkalimetal impurities from liquid diene polymers.

Patent No. 2,631,175 discloses a polymerization process whereby liquiddiene polymers are prepared using alkali metals as polymerizationcatalysts. The products produced by this process have considerableutility but further work has disclosed possibilities for improvements inthe commercial operation of the process.

In the alkali metal polymerization of conjugated dienes and the like, itis necessary to treat the resulting reaction mixture in some manner toconvert the alkali metal and reactive alkali metal organic compoundspresent to prevent further catalytic effect of the alkali metal on theproduct. Alkali metal catalysts are harmful if left in the productbecause they promote cross-linking of the polymer with concomitantformation of gel. Alkali metal hydroxides left in the polymers aredeleterious for many uses of such polymers. For instance, a liquidpolymer, which is to be incorporated in low plasticity synthetic rubberfor improving its processing characteristics, will impart too fast acuring rate of a compound of said rubber if it contains alkali metalhydroxides. A liquid polymer which is to be used as a drying oil shouldnot contain any substantial amount of alkali metal or alkali metalcompounds as these tend to render the liquid cloudy and causeundesirable reactions when compounding these oils in paints, varioustypes of varnishes and protective surface coatings and adhesiveformulations.

By the term alkali metal impurities, employed herein, it is meant toinclude free alkali metal and/or organo alkali metal compounds formedduring the polymerization and present in the polymer product, and alsoorgano alkali metal compounds employed as catalysts, such as sodiumbutyl, sodium triphenyl methyl, and the like, and alkali metal hydrides.These latter compounds are exemplary of catalysts within the groupconsisting of the alkali metals, the alkali metal hydrides, the alkalimetal alkyls, and the alkali metal aryls. Any of the abovementioned typematerials, i.e., free alkali metals such as sodium, potassium, orlithium, and/ or the defined organo alkali metal compounds, when presentin the polymer product comprise the said alkali metal impurities,removed from the polymer in accordance with this invention.

The present invention is directed to a process for recovering asubstantially catalyst free product, either as a solution of the polymerin an organic solvent or as the liquid polymer free of solvent. It haslong been known that contacting the polymerization zone eflluent with analcohol results in deactivation of the catalyst. Alcohols known in theart for such treatment include, preferably, those containing up to fourcarbon atoms per molecule such as methyl alcohol, ethyl alcohol, thepropyl alcohols, the butyl alcohols, propylene glycol and butyleneglycol.

According to prior art processes, it has been common to treat thepolymer, following treatment with the alcohol, in a water washing step.Such water was-hing produces a substantially catalyst-free product but,in some cases, leads to the formation of emulsions which reduce theultimate yield of product. Furthermore, the presence of even traceamounts of water is deleterious to filtration rates and to the ashcontent of the finished polymer.

Broadly, the present invention is directed to treatment of the polymers,commonly the process being practiced on the reaction zone eflluent, by amethod which does not involve the use of water.

The following are objects of this invention.

An object of this invention is to provide alkali metal free liquidpolymers of conjugated diolefins. A further object of this invention isto provide a process for removing alkali metal impurities from liquidpolymers of conjugated dienes. A further object of this invention is toprovide a process for the removal of alkali metal impurities fromhomopolymers of 1,3-butadiene and copolymers of 1,3-butadiene andZ-methyl-S-vinylpyridine.

Other objects and advantages of this invention will be apparent to oneskilled in the art upon reading this disclosure.

As stated, the present invention relates to liquid polymers ofconjugated dienes prepared according to the method disclosed in PatentNo. 2,631,175. As shown in said patent, the alkali metals can be used toproduce liquid polymers of good quality, said polymers having aviscosity in the range of to 6000 Saybolt Furol seconds at 100 F. Thepolymers include homopolymers of conjugated dienes containing 4 to 8carbon atoms, those containing 4 to 6 carbon atoms being preferred.Representative conjugated dienes include 1,3-butadiene, isoprene,piperylene, 2-methyl-1,3 pentadiene, 2,3-dimethyl-1,3- butadiene,2-methy-l-l,3 hexadiene, and 1,3-octadiene. Various vinylidenecontaining comonomers can be used in combination with the conjugateddiene, these including, for example, styrene, vinyl chloride,acry-lonitrile, methyl vinyl ether, and the like. A group of copolymersof current interest are those prepared by polymerizing a major amount ofa conjugated diene as above defined and a copolymerizable heterocyclicnitrogen base.

The heterocyclic nitrogen bases which are applicable are those of thepyridine and quinoline series which are copolymerizable with aconjugated diene and contain one substituent wherein R is eitherhydrogen or a methyl group, i.e., the substituent is either a vinyl oran alphamethylvinyl (isopropenyl) group. The vinyl-substitutedheterocyclic nitrogen bases of the pyridine and quinoline series whichare preferred are those having only one substituent and of thesecompounds, those belonging to the pyridine series are most frequentlyused. Various derivatives can also be used but it is generally preferredthat the total number of carbon atoms in the nuclearsubstituted groups,in addition to the vinyl or.alpha 'methylvinyl, should not be greaterthan 12 and most frequently these alkyl substituents are methyl and/orethyli where R is selected from the group consisting of hydrogen, alkyl,vinyl, alpha-methylvinyl, alkoxy, halo, hydroxy,

cyano, aryloxy, aryl, and combinations of these groups such ashaloalkyl, alkaryl, hydroxyaryl, and the like; one and only oneof thesegroups being selected from the group consisting of vinyl andalpha-methylvinyl; and the total number of carbon atoms in the nuclearsubstituted groups, in addition to the vinyl or alpha-methylvinyliginyl-S-ethoxypyridine; 2 vinyl 4,5-dichloropyridine;

Z-(alpha-methylvinyl) 4 hydroxy 6-cyanopyridine; 2- vinyl 4phenoxy-S-methylpyridine; Z-cyano-S-(alphamethylvinyDpyridine; 3vinyl-S-phenylpyridine; 2-(parainethylphenyl) 3 vinyl-4-methylpyridine;3-vinyl-5- '(hydroxyphenyDpyridine; 2-vinylquinoline; 2 vinyl-4-'ethylquinoline; 3 vinyl 6,7 di n propylquinoline; 2- inethyl-4-nonyl 6vinylquinoline; 4 (alpha-methylvinyl)-8-dodecylquinoline; 3vinylisoquinoline; 1,6-dimethyl 3 vinylisoquinoline';2-vinyl-4-benzylquinoline; 3-vinyl 5 chloroethylquinoline;3-vinyl-5,6-dichloroisoquinoline; 2-vinyl 6 ethoxy-7-methylquinoline;3-vinylfi-hydroxymethylisoquinoline; and the like. When copolymers areprepared, the diene component is generally present in a major portion byweight based on the. monomers charged. a

As previously stated, the alcohol treatment of the prior art is used inthe present invention for the deactivation of the catalyst. Thistreatment results in the formation of the corresponding alcoholate, suchas, for example, sodium methylate. The alcohol is normally used in anamount at least equivalent to that corresponding to the alkali metalpresent. v t

The next step involves treatment with carbon dioxide, the addition ofthis material producing a bulky, flocvolts per inch of electrodespacing. Such treatment removes any gel which is present in the liquidpolymer and produces a gel-free product Further details of thispurification process are available in my copending application.

An alternative process is to pass the polymer immediate 1y aftertreatment with the carbon dioxide (without preliminary filtration)through the zone wherein the direct current electrostatic field ismaintained.

This application is related to my application Serial No. 770,601, filedconcurrently herewith, which involves the use of carbon disulfide inplace of the carbon dioxide of the present invention. The choice betweenthese two types of treatment is somewhat dependent upon the method ofremoval of the precipitate following the treatment with thecarbon'disulfide or the carbon dioxide. The use of carbon dioxideresults in the production of a bulky, flo cculent or gelatinousprecipitate which settles,

if at all, very slowly from the polymer or polymer solution. Thisprecipitate is distinguished from the crystalline precipitate when usingcarbon disulfide which does settle comparatively quickly. In many cases,better filtration is obtained following the use of carbon dioxide.-Using either additive, the treatment with the direct currentelectrostatic field can be used but, since a greater volume of materialis removed therein when using the carbon dioxide, more frequent cleaningis required than when using the carbon disulfide anda settlingoperation. In the data presented in this application, treatment of acopolymer of 1,3-butadiene and 2-methyl-5-vinylpyridine is presented.This is done primarily because such a polymer represents a moreditficult purification problem than does a totallyhydrocarbonpolymersuch as the homopolymer of butadiene or a butadiene/styrene copolymer. v

' The following example presents 'data concerning a separation basedupon the present invention although, obviously, the specific numericallimits shown should not be considered unduly limiting.

i I Example A liquid copolymer of 1,3-butadiene and 2-methyl-5-vinylpyridine was prepared using a monomer ratio of 85 parts by weightbutadiene and 15 parts by weight of 2'- methyl-S-vinylpyridine. Thismaterial was polymerized at a temperature of 185 F. and a pressure of 30p.s.i.g. using finely divided sodium as the catalyst in an amount ofapproximately 1 weight percent based upon the monomers charged.Commercial grade normal heptane was used as the solvent in an amount togive an approximate 40 weight percent solution of the liquid polymer.Following polymerization, methyl alcohol was added in an amount to givea 100 percent excess based upon the sodium present. v

7 Following tthetreatment with the methyl alcohol, the mixture wascarbonated by the introduction of carbon dioxide for 1% hours at 95 F.while maintaining a pressure'of 25 p.s.i.g. .A bulky flocculentprecipitate culent or gelatinous precipitate which normally does not wsettle out of the solution but which can be removed by filtration.

An additional step which is frequently used in the purification of thepolymer is passage thereof through an electrostatic field followingpreliminary filtration. Such a process is disclosed and claimed in mycopending application Serial No. 690,182, filed October 11, 1957. Inthis process, the polymer is subjected to a direct current electrostaticfield by passing it through a vessel comprising an annular electrode anda center electrode. Either a solution or the liquid polymer itself canbe passed through this apparatus. Maintained between these electrodeslisa voltage gradient in the range of 800 to 33,000

formed and the mixture was then filtered. Used was a small pressurefilter having a three square inch filter area while maintaining apressure drop across the filter of 10 p.s.i.g. The filtrate volume atseconds was 0.5 milliliter; at 300 seconds 1.6 milliliters; at 900'seconds.3.6 milliliters; and at 1800 seconds 5.7 milliliters. Theliquid polymer, after removal of the solvent therefrom,had an ashcontent of 0.003weight percent and a viscosityof approximately 3,000Saybolt Furol seconds at 100 Without thecarbondioxide treatment, thefiltrate volume at 100 seconds was 0; at 300 seconds,0.3 milliliter; at900 seconds, 0.4 milliliter; at 1800 seconds, 0.6 milliliter; and theash content was 0.002 weight percent.

' A portion of this polymer was mixed with toluene to' give a solidscontent of 50 percent by weight. This material was coated ontocommercial electrolytic plate and baked at 390 F. for 13 minutes. Thematerial was shown to be very satisfactory as a can coating.

As shown in the example, it is preferable to add the carbon dioxide atan elevated temperature because this increases the reaction rate.Temperatures, however, can vary from as low as 50 F. up to 200 F., theexact temperature not being critical. The addition of the carbon dioxideto the alcohol treated material results in the formation of sodiummethylate. Thus, it will be seen that the amount of carbon dioxide usedshould be at least equivalent to the sodium present, and it ispreferable to use a considerable excess, as much as 100 percent, inorder to insure complete reaction. The precipitate formed is sodiummethyl carbonate.

As many possible embodiments can be made of this invention withoutdeparting from the scope thereof, it is to be understood that all matterhereto set forth is to be interpreted as illustrative and not as undulylimiting the invention.

I claim:

1. A method for treating a liquid polymer produced by polymerization ofa conjugated diene in the presence of an alkali metal catalyst and whichcontains alkali metal as an impurity, which comprises treating saidliquid polymer in the absence of water with an alcohol and thereaftercarbon dioxide, and removing the resulting precipitate from said liquidpolymer.

2. The method of claim 1 wherein said liquid polymer is a homopolymer ofliquid polybutadiene.

3. The method of claim 1 wherein said liquid polymer is a copolymer of1,3-butadiene and styrene.

4. The method of claim 1 wherein said liquid polymer is a copolymer of1,3-butadiene and Z-methyl-S-vinylpyridine.

5. A method for treating a liquid polymer produced by polymerization ofa conjugated diene in the presence of an alkali metal catalyst and whichcontains alkali metal as an impurity, which comprises treating saidliquid polymer in the absence of water with methyl alcohol andthereafter carbon dioxide, and removing the resulting precipitate fromsaid liquid polymer.

6. A method for treating a liquid polymer produced by the solutionpolymerization of 1,3-but'adiene and 2- methyl-S-vinylpyridine in thepresence of a sodium polymerization catalyst and which contains sodiumas an impurity, which comprises treating the polymerization zoneefiiuent in the absence of water with methyl alcohol in an amount atleast equal to that required to react with all sodium present,thereafter passing carbon dioxide through the mixture until aprecipitate is formed, and filtering the resulting mixture to removesaid precipitate from said polymer.

References Cited in the file of this patent UNITED STATES PATENTS1,990,213 Winkler et al. Sept. 6, 1932 2,813,136 Mertz Nov. 12, 19572,827,447 Nowlin et al. Mar. 8, 1958

1. A METHOD FOR TREATING A LIQUID POLYMER PRODUCED BY POLYMERIZATION OFA CONJUGATED DIENE IN THE PRESENCE OF AN ALKALI METAL CATALYST AND WHICHCONTAINS ALKALI METAL AS AN IMPURITY, WHICH COMPRISES TREATING SAIDLIQUID POLYMER IN THE ABSENCE OF WATER WITH AN ALCOHOL AND THEREAFTERCARGON DIOXIDE, AND REMOVING THE RESULTING PRECIPITATE FROM SAID LIQUIDPOLYMER.